Graphene, a single-atom-thick sheet consisting of sp2 hybridized carbon atoms arrayed in a honeycomb pattern, is the building block of graphitic carbons. Graphene may be viewed as an individual atomic plane of the graphite structure. Graphene as a two-dimensional nanosheet has attracted increasing interest due to its unique properties of high in-plane electronic conductivity, high tensile modulus, and high surface area, which make graphene an attractive candidate for applications in electronic devices and composite materials. Moreover, with its high surface area and good chemical stability, graphene may be used as a gas adsorbant, ultracapacitor material, or a supporting material for developing novel heterogeneous catalysts with enhanced catalytic activity.
Graphene may be produced by any one of several methods, including the straightforward exfoliation technique of manually peeling off of the top surface of small mesas of pyrolytic graphite, chemical vapor deposition on metal surfaces, epitaxial growth on electrically insulating surfaces, such as SiC, and the like. Although multiple production methods do exist, large-scale applications of graphene require simple and cost effective methods of production. Hence, the primary route in making graphene is still the exfoliation of graphite oxides followed by a chemical reduction.
In aqueous solvent dispersions of graphene prepared by chemical reduction, graphene sheets are separated by solvents stabilized by electrostatic forces associated with ionizable groups introduced during the exfoliation. However, like other dispersions of nanomaterials with high aspect ratios, after the solvent is removed from the dispersion, the dried graphene sheets (GSs) usually aggregate and form an irreversibly interconnected or tangled precipitated agglomerate. This agglomeration is driven by the van der Waals interactions between the neighboring graphene sheets, urging the graphene sheets to stack back together in a disorganized and typically haphazard fashion. This agglomeration also leads to a considerable loss of the effective surface area of graphene, which affects the graphene applications in, for example, supercapacitors, batteries, and catalyst supports, where a high surface area of active materials is desired for performance. Therefore, how to achieve the intrinsically ultra-high surface area of graphene in its solid state is of interest in advancing the applications of graphene materials.
Anchoring nanoparticles on the graphene surface before the GS's aggregation is one effective way to keep the GS's high surface area. The deposition of Pt nanoparticles on a graphene surface before drying has been shown to increase the surface area of the composite from 44 m2/g to 862 m2/g with the anchoring of the Pt nanoparticles on the surface. Graphene polyoxometalate nanoparticle composites have been observed to yield a graphene surface area of about 680 m2/g. Graphene sheet/RuO2 composites have been observed with increased surface area increases from 108 m2/g to 281 m2/g. These composites also exhibited a high specific capacitance 570 F/g and an enhanced rate capability. Although the surface area of GSs have been increased with the addition of the nanoparticles, the resulting specific surface area was still much lower than the theoretical surface area of 2630 m2/g of the isolated GSs.
Thus, there is a need for graphene materials having effective surfaces areas approaching the theoretical maximum of 2630 m2/g. Further, there remains a need for a method of reliably producing the same. The present novel technology addresses these needs.